react when should you use refs

// using refs 
class App extends React.Component { 
 constructor(){ 
  super(); 
  this.state = { sayings: ""}; 
 } 
 update(e){ 
  this.setState({ sayings: this.refs.anything.value}); 
 } 
 render(){ 
  return ( 
   <div> 
    Mukul Says <input type="text" ref="anything"
      onChange = {this.update.bind(this)}/> 
   <br/> 
   <em>{this.state.sayings}</em> 
  </div> 
  ); 
 } 
} 
 ReactDOM.render(< App />, document.getElementById('root'));